More compelling evidence in support of The Grandmother Hypothesis

During my doctoral research, I spent 10 months with 15 persons with mild to moderate dementia, half of whom volunteered with students at The Intergenerational School (TIS) in Cleveland.

I found that the experience of serving as a “mentor” for elementary school children contributed to enhanced quality of life for persons who made weekly visits to TIS.

After rigorously studying the mountains of qualitative data I had accumulated through field notes, interviews, and focus groups, I was fascinated by the revelation that many of the volunteers — particularly the women — viewed students at TIS as “proxy grandchildren”. Indeed, as most of the actual grandchildren of the participants were scattered across the United States (the mean distance between subjects and their grandkids was over 1,000 miles), the TIS students appeared to satiate the need older persons had for interaction with the young. As one participant told me, “We are all grandmothers to these little boys and girls.”

In my thesis, I explored this theme by citing a somewhat controversial theory in evolutionary anthropology called the “Grandmother Hypothesis”. In short, this theory conjectures that the late-life infertility in human females has had adaptive value over our evolutionary history; spared of child bearing responsibilities, older women could invest themselves in educating and furthering the maturation of their grandchildren to improve their survival and reproductive success.

In my thesis, I proposed that, in the absence of one’s own grandchildren, this evolutionary inclination to contribute to the furtherance of younger generations might be extended to other children in one’s proximate space, as evidenced by the increasingly substantive interactions I witnessed at TIS, and the clear benefits these relationships had on quality of life.

Today, I came across an interesting BBC news article in which Japanese researchers have observed two grandmother macaques intervening in the rearing of their own grandchildren, providing essential care and suckling the young. This is believed to be the first example of such behavior shown by a non-human primate.

The article quotes the lead researcher, Dr. Masa Nakamichi as saying:

“To our knowledge, there have been no reported cases in which, instead of a mother, a grandmother without dependent offspring has continuously provided essential care for the survival of her dependent grandchild, which is in accordance with the grandmother hypothesis.”

It should be said that while this observation does not in any way prove the “Grandmother hypothesis”, it certainly lends merit to the theory by demonstrating this complex behavior in a species that shares a closely related common ancestor with human beings.